The application generally relates to heating, ventilation, air conditioning and refrigeration (HVAC&R) systems.
Vapor compression refrigeration cycles typically require sub-cooling (i.e. cooling the refrigerant to a temperature lower than the saturation temperature at the condenser pressure) at the condenser outlet for stable operation of metering devices, such as expansion valves; sub-cooling also increases the refrigeration effect of refrigerant in the evaporator. Due to a low heat transfer coefficient of liquid refrigerants and small temperature differences between the refrigerant and the cooling fluid, the surface area of the condenser to achieve the desired level of sub-cooling can become considerable and a significant portion of the condenser surface can be dedicated to sub-cooling the refrigerant. Thus, the efficiency of the condenser, and in turn the entire system, is restricted.
Using a significant portion of the condenser surface for sub-cooling can have a negative impact on system efficiency, as surface area of the condenser that could be used for condensation is instead used for sub-cooling, resulting in a higher compressor discharge pressure being required.
More recent condenser coil technologies, such as multi-channel heat exchangers, operate at a lower condensing temperature, which reduces the temperature difference between the liquid refrigerant and air. This, in turn, increases the importance of sub-cooling in systems using such heat exchangers.
In other cases, liquid refrigerant may need to be piped over relatively long distances. As a result of the pressure drop across such distances, phase changes can occur at undesired locations, which may be avoided by first adequately subcooling the refrigerant.
Intended advantages of exemplary embodiments satisfy one or more of these needs or provide other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments that fall within the scope of the claims, regardless of whether they accomplish one or more of the aforementioned needs.